Although the induction of tumors in human beings by exposure to environmental chemical carcinogens is well-documented and we have shown that normal human cells in culture are readily mutated by such carcinogens, no one has been able to reproducibly quantitate the frequency of transformation of human cells in culture with chemical carcinogens. The advantages of being able to carry out such transformations are: 1) it would provide the closest analog we have to studying human chemical carcinogenesis in vivo; 2) it would allow us to directly test the hypothesis that a causal relationship exists between somatic cell mutation and cell transformation; and 3) it could serve as the basis for an important system for the identification of potential chemical carcinogens. Therefore, we propose to work out methods required to establish such an in vitro chemical carcinogenesis system for detecting (and, if possible, quantitating) transformation in human cells (fibroblasts and epithelial) in culture, taking into consideration the conditions that have been demonstrated to be necessary for the successful transformation of animal cell cultures. Using populations of human cell types selected because they possess characteristics similar to those of one or more of these successful animal cell systems, we will: 1) expose the cells to direct-acting "ultimate" carcinogens, using repeated doses if necessary. 2) permit subsequent cell division in order to allow for "fixation and expression of transformation." 3) identify "candidate transformants" by certain morphological and/or functional caracteristics, and 4) correlate these with the ability of the "candidate transformants" to produce tumors in athymic nude mice. We will also examine the effect of promotors on the ability of human cells to be transformed.